The present invention relates to an injection molding machine and, more particularly, an injection molding machine provided with an improved quick disconnect coupling mechanism between the plasticizing unit and drive unit which allows for quick change of the plasticizing unit.
In injection molding, it is frequently necessary to modify the thermoplastic material composition depending on the type of part being produced. In conventional machines, a change in material composition requires prolonged purging of material through the plasticizing unit when changing from one resin material to another thereby resulting in a waste of resin, energy and time.
In order to avoid the disadvantages associated with prolonged purging, it is known in the prior art to simply remove the plasticizing unit, that is the barrel and screw assembly, and to substitute therefor a clean, preheated set of components for the new resin.
U.S. Pat. 4,704,078 and U.S. Pat. No. 4,708,622 to Hehl show how a quick barrel change system can be facilitated in small injection molding machines. In the '078 and '622 patents, an injection molding machine is disclosed which has an exchangeable plasticizing unit comprising a barrel and a feed screw, a drive unit includes a spindle for imparting rotation to an actual shifting of the feed screw within the barrel. A coupling assembly is provided for operatively connecting and disconnecting the spindle of the drive unit to the feed screw of the plasticizing unit. As can be seen in FIG. 8 of the '078 patent, the coupling assembly for coupling the drive motor to the feed screw for supplying torque to the drive screw is transmitted through a drive dog 26. The main disadvantage of the drive dog design is that, for large machines where the power being transmitted from the drive motor to the screw is in the order of 50 hp or greater, the drive dog design is not sufficiently strong.
A further prior art device is disclosed in German Offenlegungsschrift No. DE 32 29 223. The '223 document discloses four different species of hydraulic couplings for connecting and disconnecting the plasticizing unit of the injection molding machine to the drive unit. The disadvantage of all of the species of hydraulic couplings is that they require a supply of pressurized hydraulic fluid to act on the screw connector in order to disengage the connector and allow for automatic screw removal. In order to supply the necessary pressurized hydraulic fluid, a complicated arrangement of seals and channels are required throughout the plasticizing unit and drive unit. The requirement for rotating seals complicates and reduces the reliability of the coupling system.
A further mechanism for quick changing of a plasticizing unit from a drive unit is disclosed in U.S. Pat. No. 4,588,365. The injection molding assembly disclosed in the '365 patent includes two separate extruder units which, by way of a switching device, can be selectively coupled and uncoupled to the drive unit of the injection molding machine. This arrangement requires a relatively complicated control system for interchanging the two extruder units.
Naturally, it would be highly desirable to provide a coupling mechanism for coupling the plasticizing unit of an injection molding machine to the drive unit there of which is simple of construction and strong enough to allow for power transmission between the drive unit and the plasticizing unit in the order of 50 hp or more.
Accordingly, it is the principle object of the present invention to provide an injection molding machine provided with an improved coupling mechanism between the plasticizing unit and drive unit which allows for quick change of the plasticizing unit from the injection molding machine.
It is a further object of the present invention to provide a coupling mechanism as aforesaid which is sufficiently strong for use on large injection molding machines.
It is a still further object of the present invention to provide a coupling mechanism as aforesaid which is of simple construction, economic to manufacture and easily used with a high degree of reliability.
Further objects of the present invention will appear hereinbelow.